The present invention relates to an Otto cycle engine. Particularly, it relates to a supercharged Otto cycle engine. It is well-known that a turbosupercharger which have been used for many years are capable of high-pressure-ratio supercharging.
In general, under a high pressure ratio, knocking is inherent in an Otto cycle gasoline engine since the compression temperature of the charge as well as the temperature at the compression end is high in spite of cooling by a charge cooler. Reducing the compression ratio to avoid knocking causes a decrease in thermal efficiency which leads to an increase in fuel consumption. Also, if the supercharged pressure is reduced in order to prevent the knocking, a big output power cannot be obtained. This, of course, does not attain the primary object of the supercharger. The above noted defects have caused a great difficulty in the development of supercharged Otto cycle engines.